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Measured Spectra (measured + spectrum)
Selected AbstractsRapid estimation of chemical kinetics by implicit calibration.JOURNAL OF CHEMOMETRICS, Issue 2 2003Abstract This study continues the development of a method, implicit calibration, for estimating kinetic parameters from on-line measurements of batch reactions. The basic idea of implicit calibration is to combine non-linear parameter estimation with the calibration of measured spectra with concentrations calculated by an assumed kinetic model. A new example is studied, an esterification reaction with a rather complicated kinetic mechanism, where activities, instead of concentrations, and NIR spectra are used as measurements. The emphasis in the study is on estimating the uncertainty of the kinetic parameters. Two approaches, linearization and bootstrap, are applied. In the case studied, the two approaches give closely similar estimates of the uncertainty. As well, a new way is introduced to control the rigidity of the implicit calibration, based on minimizing the lack of fit of the model. It is also shown that ,mixed implicit calibration', i.e. implicit calibration combined with a few off-line calibrated concentrations, greatly enhances the identifiability of the kinetic model. Copyright © 2003 John Wiley & Sons, Ltd. [source] Fast principal component analysis of large data sets based on information extractionJOURNAL OF CHEMOMETRICS, Issue 11 2002F. Vogt Abstract Principal component analysis (PCA) and principal component regression (PCR) are routinely used for calibration of measurement devices and for data evaluation. However, their use is hindered in some applications, e.g. hyperspectral imaging, by excessive data sets that imply unacceptable calculation time. This paper discusses a fast PCA achieved by a combination of data compression based on a wavelet transformation and a spectrum selection method prior to the PCA itself. The spectrum selection step can also be applied without previous data compression. The calculation speed increase is investigated based on original and compressed data sets, both simulated and measured. Two different data sets are used for assessment of the new approach. One set contains 65,536 synthetically generated spectra at four different noise levels with 256 measurement points each. Compared with the conventional PCA approach, these examples can be accelerated 20 times. Evaluation errors of the fast method were calculated and found to be comparable with those of the conventional approach. Four experimental spectra sets of similar size are also investigated. The novel method outperforms PCA in speed by factors of up to 12, depending on the data set. The principal components obtained by the novel algorithm show the same ability to model the measured spectra as the conventional time-consuming method. The acceleration factors also depend on the possible compression; in particular, if only a small compression is feasible, the acceleration lies purely with the novel spectrum selection step proposed in this paper. Copyright © 2002 John Wiley & Sons, Ltd. [source] Some aspects of SERS temporal fluctuations: analysis of the most intense spectra of hydrogenated amorphous carbon deposited on silverJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2007Andrzej Kudelski Abstract Surface-enhanced Raman scattering (SERS) spectra of hydrogenated amorphous carbon (aC:H) deposited on silver substrates have been recorded with a confocal Raman microscope. When scattered radiation is collected during a short time from an area of a few square micrometres, the subsequently measured SERS spectra often exhibit strong temporal changes (fluctuations). In this paper we present examples of spectra for which the intensity maxima of the fluctuating narrow Raman bands are significantly higher than that of the background (the background is usually dominated by two broad Raman bands centred at about 1350 and 1590 cm,1). In a series of successively measured spectra, one can find spectra with noticeably different total integral intensity. This suggests that the results of averaging the spectra revealing strong and weak fluctuations may be different (at least in intensity). The influence of some electrolytes on the SERS spectral fluctuations is also analysed. Our experiments revealed that the efficiencies of quenching of the SERS spectral fluctuations by various electrolytes are significantly different. We suggest that only anions directly interacting with the metal surface quench strong SERS fluctuations, and that the large differences between chloride and perchloride solutions are caused by differences in the strength of interaction of Cl, and ClO4, anions with the silver surface. Copyright © 2007 John Wiley & Sons, Ltd. [source] Bullous pemphigoid detection by micro-Raman spectroscopy and cluster analysis: structure alterations of proteinsJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2005Erez Azrad Abstract In this study, micro-Raman spectroscopy was used, for the first time, to detect spectral changes between healthy and diseased skin tissues with bullous pemphigoid (BP). The spectral changes provide information about the biochemical alterations between normal skin and blistered and nonblistered regions in samples diagnosed histopathologically as BP. Raman spectra, characterized by many peaks, revealed the molecular composition of the different skin layers, stratum corneum, epidermis and dermis of normal skin. Comparison of spectra monitored at the dermoepidermal junction (DEJ) of healthy skin with those of blisters caused by BP showed evidence for large variations in the amide I and III regions. The alterations of the protein content, amide I and III, are a result of the appearance of immunoglobulin G (IgG) and fibrin, characteristics of BP. Indication for the disease at early stages was obtained from changes in protein content, evidenced in the measured spectra assisted by cluster analysis. The method employed here can contribute to the nearly real-time diagnosis and to a better understanding of the physical and biomolecular processes effected by BP, and might have implications on other skin diseases. Copyright © 2005 John Wiley & Sons, Ltd. [source] Calculation of XANES/ELNES Spectra of All Edges in Si3N4 and Si2N2OJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002Wai-Yim Ching Using a recently developed first-principles supercell method that includes the electron and core-hole interaction, the XANES/ELNES spectra of Si- L2,3, Si- K, and N- K edges in ,-Si3N4, ,-Si3N4, spinel c -Si3N4, and Si2N2O were calculated and compared. The difference in total energies between the initial ground state and the final core-hole state provides the transition energy. The calculated spectra are found to be in good agreement with the experimental measurements on ,-Si3N4 and c -Si3N4. The differences in the XANES/ELNES spectra for the same element in different crystals are explained in terms of differences in local bonding. The use of orbital-decomposed local density of states to explain the measured spectra is shown to be inadequate. These results reaffirm the importance of including the core-hole effect in any XANES/ELNES spectral calculation. [source] The local isotropy hypothesis and the turbulent kinetic energy dissipation rate in the atmospheric surface layerTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 603 2004M. Chamecki Abstract We test the applicability of the local isotropy hypothesis to surface-layer turbulent flow; turbulent velocities measured with a three-dimensional sonic anemometer are used for this purpose, and the predictions of local isotropy for the spectra, second- and third-order structure functions are assessed against measured data. Also investigated are scale interactions via the correlation between velocities and velocity increments, and the ability of isotropic spectral models to reproduce measured spectra. In general, second-order structure functions display a narrower inertial range than the corresponding spectra; both the known effects of path-averaging and the predictions of the spectral models show that the sonic anemometer is unable to resolve the whole inertial range, even at a measurement frequency of 60 Hz. We confirm previous results that unstable runs tend to be more isotropic, but find that, for third-order statistics, isotropy does not hold well for the data analysed. Turbulence intensity, and not atmospheric stability, plays a determining role on the correlation coefficient between velocities and velocity increments. The observed anisotropic behaviour has important implications for the calculation of the turbulent kinetic energy dissipation rate from Kolmogorov's four-fifths law, whose estimates are consistently smaller than those from the inertial range of the spectrum or the structure functions. Copyright © 2004 Royal Meteorological Society [source] Raman spectroscopy of secondary structure of elastinlike polymer poly(GVGVP)BIOPOLYMERS, Issue 3 2001Pavel Schmidt Abstract Raman spectra of the elastinlike polypentapeptide poly(GVGVP) were measured in H2O and D2O as solutions and, after increasing the temperature, as suspensions and sediments. In addition, spectra of the polypentapeptide in the solutions of increasing concentration and in the solid state were also investigated by gradually evaporating the water. Significant changes in band frequencies, intensities, and shapes were found for selected Raman bands in the measured spectra, particularly for the CH stretching, the glycine CH2 wagging, and some amide vibrations. The CH stretching vibrations are influenced predominantly by the presence of water, the glycine CH2 wagging vibrations are associated with conformational transitions. Three possible types of poly(GVGVP)s in the presence of water were indicated: polymer chains in a relatively extended state in the solution, a ,-spiral structure in the suspension, and irregularly bent chains in the sediment. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 150,157, 2001 [source] Application of extended inverse scatter correction to mid-infrared reflectance spectra of soilJOURNAL OF CHEMOMETRICS, Issue 5-7 2005Neal B. Gallagher Abstract Scattering artifacts adversely affect infrared reflectance measurements of powders and soils, and extended inverse scatter correction (EISC) is a flexible method useful for correcting these artifacts. EISC was used to correct mid-infrared reflectance spectra of two different soils coated with dibutyl phosphate and the results were examined using regression analysis. To obtain the correction, EISC fits a measured spectrum to a reference spectrum. However, if measured spectra contain features not included in the reference spectrum the fit can be biased resulting in poor correction. Weighted and robust least squares were used to account for these potential biases. Additionally, the present work demonstrates how analyte-free samples can be used to determine basis functions for an extended mixture model used in the correction. Corrected spectra resulted in partial least squares models that performed at least as well as 2nd derivative spectra and were more interpretable. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||